1. Technical Field
The present invention relates to a semiconductor device and a manufacturing method of the same.
2. Related Art
MOSFETs (metal oxide semiconductor field effect transistors) using a semiconductor mainly made of gallium nitride (GaN) are known as semiconductor devices (semiconductor elements). This GaN-based MOSFET includes a semiconductor layer mainly made of GaN, a gate insulating film formed on the semiconductor layer and a gate electrode formed on the gate insulating film. The MOSFET is required to ensure sufficient channel mobility and reduce gate leakage current. The channel mobility denotes the mobility of a carrier moving through a channel area of the semiconductor layer. The gate leakage current denotes the electric current flowing from the semiconductor layer across the gate insulating layer to the gate electrode.
JP 2008-103408A describes a technique of forming a second gate insulating film made of an oxide on a first gate insulating film made of silicon nitride in a GaN-based MOSFET, in order to suppress a decrease in channel mobility due to formation of the gate insulating film. The method employable for formation of the first gate insulating film described in JP 2008-103408A is catalytic chemical vapor deposition (Cat-CVD).
JP 2013-74069A describes a technique of forming an oxide film that is a p-type semiconductor between an upper insulating film and a lower insulating film provided as a gate insulating film in a GaN-based high electron mobility transistor (HEMT), in order to reduce the gate leakage current. The methods employable for formation of the upper insulating film and the lower insulating film described in JP 2013-74069A are atomic layer deposition (ALD), plasma-enhanced chemical vapor deposition (plasma CVD) and sputtering.